Filter apparatus



2 Sheets-Sheet 1 Filed May 1, 1

IN VEN TOR. STEVEN S. DAVIS fi flgw v ATTORNEY July 26, 1966 s. s. DAVIS FILTER APPARATUS 2 Sheets-Sheet 2 Filed May 1, 1963 will/11m INVENTOR.

STEVEN S. DAVIS ATTORNEY FIG.

United States Patent 3,262,576 FILTER APPARATUS fiteven S. Davis, Bountiful, Utah, assignor to The Eimco Corporation, Salt Lake City, Utah, a corporation of Delaware Filed May 1, 1963, Ser. No. 277,294 Claims. (Cl. 210-401) This invention relates generally to filtration equipment and more specifically to filters using filter media in the form of an endless web or belt.

Filters of the endless web type are typified by those employing in the filtration section a vacuum filter drum about which the web is trained and which actually serves as the driving force moving the web whereby successive portions of the web pass over the drum and spaced apart rolls. In such filters a cake is formed on the web in place on the filter drum, the web is removed from the drum, thence is carried to the spaced-apart rolls where the cake is discharged, corrective alignment is effected, and the web is washed, following which it is returned to the drum.

As the web leaves the drum, it carries a considerable weight of moist filter cake. This causes sagging of the web with the result that the longitudinally central portion thereof must travel for a greater distance than do the edge portions. However, since the web is driven as an entity, the rate of travel of the center and edge portions are the same hence, the central portion of the web is forced to lag behind the edge portions. Unless corrective measures are employed, the inevitable result is the creation of an edge to edge how that increases in severity as the filtration cycles are repeated and which eventually will result in wrinkling of the web with consequent damage to the web and operation of the filter.

This phenomena is called mooning or biasing and is a serious obstacle to continuous filtration in endless web filters. The problem is referred to as mooning and the corrective measures as dc-mooning.

Prior de-mooning efforts have included the use of full stationary support means which seek to prevent the condition by supporting the web to eliminate sagging.

Although such an arrangement is theoretically sound, it is not practical in commercial operation.

For instance, a full stationary support under the web to prevent sagging is objectionable from the standpoint of cost, frictional wear on the medium, and the fact that localized frictional resistance of the support will itself contribute to mooning.

It is the primary objection of the present invention to provide .means compensating for mooning as it occurs on moving filter webs.

A further object is the provision of de-mooning means which, once adjusted, are capable of continuous operation without further attention.

A still further object is the provision of apparatus for carrying out the foregoing objects, which apparatus comprises a simple roll of critical configuration jou-rnalled to be freely rotatable by friction of the web passing thereover.

A related object of equal importance is the provision of a construction of the type described which, in addition to carrying out the aforementioned objects, simultaneously subjects the web to a transverse stretching action thereby eliminating wrinkles and maintaining the web at its maximum effective width.-

The foregoing and possibly other objects of the invention are attained by a freely rotatable roll mounted in the path of the moving Web and over which the web passes. The roll has a concave surface formed as it tapers fmm a minimum diameter in its central portion to maximum diameters adjacent its opposite ends; and is of construction such that the degree of taper as well as the distance between the maximum diameter opposite end portions are adjustable. By this arrangement, the distance traveled by the edge portions of the Web is adjusted to be equal to the distance traveled by the central portion to the end that the mooning effect is neutralized.

In order that the invention may be more readily understood and carried into effect, reference is made to the accompanying drawings which are offered by way of illustration only and are not to be taken as limiting the invent-ion, the scope of which is defined by the appended claims rather than by any preceding description.

In the drawings:

FIG. 1 is a perspective view of an endless web rotary drum filter embodying a preferred form of the invention, certain elements being shown in dotted lines for purposes of clarity.

FIG. 2 is a partial front view showing the essential structure of the zde-mooning roll of FIG. 1, a portion being cut away to facilitate a better understanding of the structure.

FIG. 3 is a line drawing illustrating diagrammatically travel of the'web as viewed from the side.

FIG. 4 is a view similar to FIG. 3, but taken as looking down onto the surface of the web.

In the drawings, there is shown a filter, generally designated 10, comprising a drum Ill mounted for rotation in a slurry tank 12 and driven in conventional manner as by a drive 13-.

The filter medium, in the form of anendless belt or web 14, is trained successively about the drum 1-1, a de-mooning roll 15, a discharge roll 116, an alignment correction roll .17 and tension and return roll 18.

As is best illustrated in FIG. 2, the de-mooning roll is a concave structure tapering outwardly from a central portion of minimum diameter toward the opposite end portions of maximum diameter. In the embodiment shown, the roll comprises a central shaft 21 journalled for rotation in suitable bearings 22 carried by an adjustable bracket 23 mounted on an end wall extension 19 of the filter tank; and the concavity or outward taper of the roll is provided by truncated conical portions 24 mounted on the opposite end portions of the central shaft to be axially adjustable thereon to be fixed in a selected location by suitable set screws, such as indicated at 26.

Such a construction permits adjustment of the roll to accommodate webs of varying characteristics as well as changing operating conditions. Proper location of the conical sections is determined empirically during initial stages of operation, but once the proper setting is detenmined, further adjustment is unnecessary unless conditions such *a tension, cake weight, web fabric, etc., change radically.

Behavior of the web as it undergoes mooning and the corrective influence of the de-mooning roll of the in-.

vention are illustrated by the line drawings of FIGS. 3 and-4.

When the Web is taken from the drum it is burdened with moist filter cake 20, the weight of which causes the web to sag as is to be expected. This sagging is most pronounced at the central portion 14 of the web compared to the edges 14", while intermediate portions sag proportionately. That is to say, there is a gradient as to the degree of sag between the center and edge portions of the web. The action of the concave roll is two fold. First, it supports the web to temporarily eliminate the sag, and then it lifts the web edges above the center to make them travel an extended path of distance equal to the extended path traveled by the center of the web during the sagging. In other words, the edges are lifted above their normal travel a distance equal to that which the center has saggcd below the path of normal travel of the edges.

Since the mooning stems directly from the sagging, there is a proportionate gradient in the degree of mooning across the web face. This is best illustrated in FIG. 4 where the dotted lines 25 may be visualized as a single weft or cross-thread in successive positions and corresponding degrees of mooning as the web moves from right to left in the drawings.

It will be noted that as the web progresses across the open space between the drum and de-mooning roll, the individual weft lags behind in the center, but this lagging central portion catches up to and passes the edge portion as the Web closes on and passes over the de-mooning roll. Then, during passage over the second open area between the de-mooning and discharge rolls, the center portion again lags until it comes back into alignment with the edge portions. Thereafter, and for the rest of the cycle, there is only insignificant mooning because the weight of the cake has been removed.

Although the mooning and de-mooning have been described as separate occurrences to better illustrate functioning of the invention, there actually is an overlap of these two phases. The mooning and de-mooing forces work simultaneously. However, during one part of the travel, mooning is the predominate influence while in another part of the travel (closest to the roll) de-mooning is the predominate influence. With proper adjustment of the roll, the result is a neutral or zero mooning position when the web passes the center of the de-mooning roll, and again at the point of cake discharge.

Location of the de-mooning roll in an intermediate poistion, as illustrated, is convenient and indeed preferred in many cases because of the support given the web to insure against permanent stretching under the cake weight. However, it is to be understood that the desired neutralizing effect may be obtained by locating the roll in other places in the cycle such as utilizing it as the discharge roll. In any such alternate location, suitable pre-adjustment of the conical section may be required to attain the desired result; and such adjustment can, as previously explained, be realized by axial adjustment of the conical sections within the range of their dimensions. Obviously, for adjustments outside such range, cones of different dimensions may be employed.

Another very important feature of the invention is the transverse stretching or smoothing action exerted on the web by the de-mooning roll. This action is due to the tendency of the web to climb toward the highest part of the truncated cones which insures an outward stretching force on the web as indicated by the transverse arrows on FIG. 2. This is highly desirable because it guards against wrinkles which might otherwise occur due to bunching of the web in the center. Moreover, the stretching from opposite sides of the web works favorably against incipient mooning.

The invention lends itself to use in an almost endless variety of ways, thereby coping with numerous problems such as corrosion, uneven stretch or wear of the medium. This facility is important in light of the fact that filter webs are selected more for their filterability characteristics and corrosion resistance than for stability. The ability to control such fragile webs without stretching, biasing, mooning, or excessive frictional wear is economically advantageous.

From the foregoing, it is evident that the present invention presents novel means overcoming the deleterious effects of mooning on traveling webs and is of particular A. advantage in embodiments in combination with industrial filters where carrying of the wet filter cake by the web contributes directly to mooning of the web.

I claim:

1. In a filter of the type having an endless web filter medium trained to pass successively over a filtration section, an intervening space and a discharge section, the improvement enabling compensation for the lag occurring in the transversely central portions of the medium during its travel across the intervening space between said filtration section and said discharge section, said improvement comprising an elongated rigid roll rotatably mounted in said intervening space transversely to the path of said medium in a location to supportingly engage the filter medium passing thereover, and said roll being formed with a concave surface extending substantially from end to end thereof.

2. In a filter of the type adapted to employ an endless web filter medium trained to pass successively over a filtration section, an intervening space and a discharge section, the improvement enabling compensation for the lag occurring in the transversely central portion of a medium during its travel across the intervening space between said filtration section and said discharge section, said improvement comprising an elongated rigid roll rotatably mounted in said intervening space transversely to the path of said medium in a location to supportingly engage the filter medium as it passes thereover, and said roll having a concave outer surf-ace formed by a cylindrical center member and a pair of axially aligned truncated cone members mounted concentrically on said center member adjacent the opposite ends thereof and having their apex ends directed toward each other.

3. A filter according to preceding claim 2 in which said truncated cone members are axially slideable on said cylindrical center member and there are provided locking means to secure said cone members in selected positions.

4. Sag compensating apparatus for filters of the type having an endless web filter medium trained to pass successively through a filtration section for filter cake formation, an intervening cake transport space and a discharge section for cake removal, said sag compensating device comprising a rotatably journalled, concave surfaced, rigid roll mounted with its axis transverse to the travel of said filter medium and positioned to have said medium pass thereover at a location remote from said filtration section, and means enabling adjustment of said roll toward and away from said medium.

5. In a filter of the type having an endless web filter medium trained to pass successively over a rotary filter drum and a discharge roll spaced from said drum, improved means enabling compensation for sag occurring in said'filter medium during its travel between said drum and said spaced apart roll, said means comprising a rigid concave-surfaced roll rotatably mounted between said drum and said roll in spaced parallel relationship thereto and located to supportingly engage said filter medium as it passes thereover.

References Cited by the Examiner UNITED STATES PATENTS 2,812,064 11/1957 Siebenthal 210-391 3,017,997 1/1962 Hawkes et al. 210-401 3,120,492 2/1964 Peterson 2lO-401 REUBEN FRIEDMAN, Primary Examiner.

S. ZAHARNA, Assistant Examiner. 

1. IN A FILTER OF THE TYPE HAVING AN ENDLESS WEB FILTER MEDIUM TRAINED TO PASS SUCCESSIVELY OVER A FILTRATION SECTION, AN INTERVENTING SPACE AND A DISCHARGE SECTION, THE IMPROVEMENT ENABLING COMPENSATION FOR THE LAG OCCURRING IN THE TRANSVERSELY CENTRAL PORTIONS OF THE MEDIUM DURING ITS TRAVEL ACROSS THE INTERVENTING SPACE BETWEEN SAID FILTRATION SECTION AND SAID DISCHARGE SECTION, SAID IMPROVEMENT COMPRISING AN ELONGATED RIGID ROLL ROTATABLY MOUNTED IN SAID INTERVENTING SPACE TRANSVERSELY TO THE PATH OF SAID 